1. Field of the Invention
The present invention relates to a control system for an engine and an automatic transmission for an automotive vehicle, so adapted as to reduce torque of the engine at the time of a shift of the automatic transmission.
2. Description of the Related Art
For instance, as disclosed in Japanese Patent Publication Laid-open (kokai) No. 55-46,095, it is known of a control system so adapted as to reduce torque of an engine by controlling the timing of ignition or the like, in order to suppress a torque shock from occurring due to a shift of a gear ratio at the time of a shift of the automatic transmission having a multi-stage shift mechanism.
Such a conventional control system for the engine and the automatic transmission is so arranged as to alter a shift stage in accordance with a variation in a running state of the vehicle to be determined by an angle of opening of a throttle valve, a vehicle speed or the like, on the basis of a shift map in which a shift line is predetermined. Further, such a control system is adapted to perform the control for reducing the torque of the engine at the time of a shift of the automatic transmission. The amount of the torque to be reduced is set on the basis of a map of the angle of opening of the throttle valve or the like in accordance with the shift map, and the map is so predetermined as to give an appropriate amount of the torque to be reduced at a constant shift point.
It can be noted that, for such a control system, a preset amount of the torque to be reduced becomes a value so adapted as to comply with a requirement for the amount of the torque reduced, if no shift point deviates and the absorbed inertia and the torque of the engine at the shift point is not varied due to an exterior factor, when the shift is performed. However, for instance, if the shift point is caused to deviate in accordance with changes of modes or other conditions, the amount of the absorbed inertia at the time of the shift is caused to vary in association with such changes, thereby causing a required amount of the torque reduced to vary, too. Hence, in these cases, the preset amount of the torque to be reduced may deviate from the required amount thereof, thereby impairing a feeling of the shift of the automatic transmission.